Josie Huang, who was reporting for LAist and NPR affiliate KPCC, was filming the scene as a crowd yelled at officers guarding the St Francis Medical Centre in Lynwood.
It comes after the two deputies were shot by an assailant in Compton on Saturday night.
Ms Huang can be seen in video footage being held against the crowd while she is handcuffed then placed inside a patrol car.
In a post on Twitter, Ms Huang shared video of the scene moments before her arrest early on Sunday morning.
The Los Angeles Sheriff’s Department said in a statement on social media that Ms Huang "did not identify herself as press and later admitted she did not have proper press credentials on her person" though she was wearing press credentials around her neck.